It has been known that a polymer obtained by bulk polymerization of a cycloolefin monomer in the presence of a metathesis polymerization catalyst is low in dielectric constant, dielectric loss tangent and water-absorbing ratio and excellent in mechanical strengths and heat resistance. Therefore, a cycloolefin bulk polymer with these features has been employed in various kinds of fields such as structural materials, optical parts, automobile parts, packaging materials and the like, and extremely preferably used as materials of electric or electronic parts.
In recent years, development has been requested of a multilayered high density substrate in which various kinds of elements such as a magnetic part, a capacitor and a semiconductor device are built in a circuit substrate. For the multilayered high density substrate which is able to build in a capacitor, used is a multilayer structure including a high dielectric constant layer. In order to achieve a circuit substrate for higher-speed use, a high frequency current is used, and therefore it has been required to reduce a transmission loss in proportion to a dielectric loss tangent. In a circuit substrate where various kinds of parts are surface mounted or built in, linear expansion coefficient of a metal such as semiconductor parts and wiring, and of an organic material are widely different, therefore it causes a breakage of parts and a disconnection of wiring by a environmental changes. Hence, materials with a high dielectric constant and a low linear expansion coefficient have been required in addition to conventional demand characteristics such as a low dielectric loss tangent, a high heat resistance and a low water-absorbing ratio.
In order to achieve a high dielectric constant, a low linear expansion coefficient, a high rigidity and the like, various methods have been proposed, a typical one of which is to mix a filler and a fiber reinforcement into a cycloolefin monomer. Japanese Patent Nos. 2755642, and 2859300, and Japanese Patent Application Laid-Open (JP-A) No. 9-183833 disclose that, by using a specific silane coupling agent, it is possible to reduce the viscosity of the composition when a filler is added, and to improve a rigidity of a bulk polymer obtained. However, when a large amount of the filler is mixed to satisfy the demand of a high dielectric constant and a low linear expansion coefficient, it causes a increase of viscosity of the polymerizable composition, and operability such as injection of the composition into a mold is worsened. Moreover, since bubbles generated in molding are included in a molded product (so called “bubble inclusion” occurs), a mechanical strength of the molded product is lowered or gets unevenness.
JP-A No. 2002-179889 discloses that when a monomer-soluble dispersant such as a silane coupling agent, a titanate coupling agent or a surfactant is employed, a low viscosity can be realized even if a large amount of a filler is mixed into a cycloolefin monomer. However, adding these filler has a problem to increase a dielectric loss tangent.